Hypothyroid Dogs, What Are the Signs? Which Breeds Are Likely to Develop Hypothyroidism? Which Don't?

The thyroid gland helps a dog have a good, even supply of energy, rather like a carburetor helps a car burn gasoline evenly. Just like a car’s carburetor can malfunction and need adjustment, a thyroid can go wrong and need adjustment. The two most common ways for a thyroid to malfunction are to make too much hormone (this is what usually happens in cats and is called hyperthyroidism) or to make too little hormone, which is what commonly happens in dogs and is called hypothyroidism.

With hypothyroidism, the thyroid gland stops making the hormone thyroxin and since thyroxin travels throughout the body, and can enter right into the nucleus of most cells, hypothyroidism is characterized by widespread cell inactivity. We see this inactivity in the skin, eyes, behaviour, blood, balance, and heart.

Signs & Symptoms of Hypothyroidism
When cells in the skin are inactive, the hair becomes dull then falls out; hypothyroid dogs have thin coat or even bald patches on their sides and tail. When cells in the liver are inactive, cholesterol from the food isn’t converted into useful materials and the amount of blood cholesterol becomes so high that clumps of cholesterol are deposited throughout the body, including in the eyes. Patches of cholesterol in the cornea of the eye are called corneal dystrophy.  When cells in the brain are inactive, dogs become sluggish, and many behave abnormally; a small percentage even become aggressive. Hypothyroidism is one of the most common causes of irritability in senior dogs.

When cells in the dog’s bone marrow are inactive due to hypothyroidism, no new red blood cells are made, and the dog becomes anemic. Anemic dogs are listless, don’t enjoy going for walks, and stop playing with toys.

Hypothyroid dogs can also stop playing and wanting to go for walks because their nerves are affected. When hypothyroidism affects nerve cells, dogs can have a few nerves  affected so they develop a head tilt (8th cranial nerve) or bizarre eye motions (3rd 4th & 6th cranial nerves), or hypothyroidism can affect the whole spinal cord. If the entire cord is affected, dogs can lose ability to walk normally (ataxia) and may lose the ability to know where their feet are in space (loss of proprioception).

Breeds Predisposed to Develop Hypothyroidism
If you’re seeing any of these signs in your pet, please ask for a blood test to check for hypothyroidism.  If you don’t see signs, but if you have an English Setter, request tests for hypothyroidism because more than ¼ of English Setters inherit this disease. Other breeds with high levels of inherited thyroid disease include:

Dalmatian 16.8%

Basenji 16.3%

Rhodesian Ridgeback 16.1%

Old English Sheepdog 15%

Boxer 13.8%

Maltese 13.5%

Chesapeake Bay Retriever 13.5%

Beagle 13.4%

Cocker Spaniel 12.6%

Shetland Sheepdog 12.5%

Siberian Husky 12.3%

Border Collie 11.9%

Akita 10.8%

Golden Retriever 9.1%

Breeds That Seldom Develop Hypothyroidism
In contrast, some dog breeds seldom have inherited tendency to hypothyroidism. The following breeds have about 5% or less

German Shepherd Dog 5.4%

Labrador Retriever 5.1%

Collie 5.1%

Poodle 4.4%

English Bulldog 3.9%

Dachshund 3.7%

English Springer Spaniel 3.7%

Shih Tzu 3.6%

West Highland White 3.5%

Chihuahua 2.9%

Lhasa Apso 2.8%

Pomeranian 2.7%

Miniature Pinscher 2.5%

Cairn Terrier 2.5%

Basset Hound 2.5%

Schnauzer 2.3%

Yorkshire Terrier 2.3%

Boston Terrier 2.1%

Norwegian Elkhound 2.1%

Greyhound 2.0%

Portuguese Water Dog 2.0%

Newfoundland 1.9%

Bichon Frise 1.4%

Welsh Corgi 1.3%

Miniature Schnauzer 1.2%

Cavalier King Charles Spaniel 1.1%

Flat-Coated Retriever

 

Treating Hypothyroidism
Here, we’ve covered which dogs are most likely to develop hypothyroidism and what signs and symptoms are evident. In another Caring for Pets entry, we’ll cover what we can do to treat dogs with hypothyroidism, including what to feed, what to avoid feeding, hormones & herbs.